The present invention relates to a contact lens material having excellent transparency, high oxygen permeability and high heat resistance (high glass transition temperature), and moreover having excellent ultraviolet-ray absorbing property and excellent forming and processing property.
Conventionally, excellent oxygen permeability has been required for a contact lens as one of important physical properties because there is a necessity to supply a cornea with sufficient amount of oxygen through the contact lens so that functions of metabolism of corneal tissue would not be lowered.
Also, in order to avoid that bad influences owing to ultraviolet rays are exerted upon eyes, there has been proposed a contact lens in which an ultraviolet-ray absorbing agent is used. However, this contact lens has a problem in safety because the ultraviolet-ray absorbing agent easily elutes from the contact lens.
Accordingly, it is desired that an contact lens material which has transparency, improved oxygen permeability and heat resistance, and is excellent in ultraviolet-ray absorbing property is developed without using any ultraviolet-ray absorbing agent.
U.S. Pat. No. 5,049,156 and U.S. Pat. No. 4,955,900 disclose polyimides which are used in an intra-ocular lens. However, since the polyimides absorb not only ultraviolet rays but also visible rays, that is, rays having a wavelength of at least about 380 nm, the polyimides show bad transparency.
An object of the present invention is to provide a contact lens material having excellent transparency and high oxygen permeability.
Another object of the present invention is to provide a contact lens material having excellent forming and processing property as well as high heat resistance.
A further object of the present invention is to provide a contact lens material which efficiently absorbs ultra-violet rays having wavelengths of 320 to 280 nm (UV-B) and at most 280 nm (UV-C).
These and other objects of the present invention will become apparent from the description hereinafter.